The gallbladder primarily stores which substance?

The gallbladder plays a vital role in the digestive system, specifically in the storage and concentration of bile. Bile is a digestive fluid produced by the liver, which is essential for the emulsification and digestion of fats. When food containing fat enters the small intestine, the gallbladder contracts and releases stored bile into the intestinal tract, facilitating the breakdown of fats for absorption.

Amino acids, glycogen, and insulin serve distinct functions in the body but are not stored within the gallbladder. Amino acids are the building blocks of proteins and are primarily absorbed into the bloodstream from the digestive tract; glycogen is a form of stored energy primarily found in the liver and muscle tissues; and insulin is a hormone produced by the pancreas to regulate blood sugar levels. Thus, the gallbladder’s primary function is the storage of bile, making it the correct choice in this context.